Method and apparatus for a variable rate pipe on a linear connection

ABSTRACT

A method and apparatus for a variable rate pipe on a linear connection. In one embodiment of the invention, a method comprises provisioning a pipe from a part of a working channel and at least part of a protection channel of an M:N linear connection, load balancing layer 2/3 traffic transmitted in the pipe while there is not a failure, reducing the pipe&#39;s bandwidth when the failure occurs in the M:N linear connection, load balancing layer 2/3 traffic for the reduced pipe; and transmitting the load balanced layer 2/3 traffic in the reduced pipe while there is the failure.

NOTICE OF RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/887,299, titled Method and Apparatus for Variable RatePipes, filed on Jun. 22, 2001, which claims priority to U.S. ProvisionalPatent Application Ser. No. 60/258,765, titled Method and Apparatus forVariable Rate Pipes, filed on Dec. 30, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to communication networks. More specifically, thepresent invention relates to communication over optical networks.

2. Description of the Related Art

Current networks must satisfy consumer demand for more bandwidth and aconvergence of voice and data traffic. The increased demand of bandwidthby consumers combines with improved high bandwidth capacity of corenetworks to make edge networks a bottleneck despite the capacity ofoptical networks.

Multiplexing is used to deliver a variety of traffic over a single highspeed broadband line. An optical standard such as Synchronous OpticalNetwork (SONET) or Synchronous Digital Hierarchy (SDH) in conjunctionwith a multiplexing scheme is used to deliver various rates of trafficover a single high speed optical fiber. SONET/SDH is a transmissionstandard for optical networks which corresponds to the physical layer ofthe open standards institutes (OSI) network model. One of the protectionschemes for SONET/SDH involves automatic protection switching (APS) in abi-directional line switched ring (BLSR) architecture. BLSR utilizeslinear switching to implement APS.

FIGS. 1A-1E are diagrams illustrating an example of traffic flow in aBi-Directional Line Switched Ring (BLSR) while there is and is not afailure in the ring. FIG. 1A is a diagram of exemplary traffic flow onthe ring while there is not a failure. Although a BLSR has a workingchannel and a protection channel for traffic flowing East and West, onlyone working channel and its protection channel (which traverse the ringin the opposite direction) are shown in FIGS. 1A and 1B. In FIG. 1A, anoptional ring includes nodes 101, 103, 105, 111, 109, and 107 clockwise.In FIG. 1A, a stream of time division multiplex (TDM) traffic 113 isreceived from a source external to the ring at node 101. Node 101transmits this traffic 113 over its East span 115 on a working channel119 to a node 103. Node 103 transmits the traffic 113 over its East span117 in a working channel 121 to node 105. The stream of TDM traffic 113exits the ring at node 105 to a destination external to the ring.Although extra traffic may be flowing in the protection channels of thering, only the stream of TDM traffic 113 is shown for simplicity.

FIG. 1B is a diagram of exemplary traffic flow on the ring while thereis a failure. In FIG. 1B, the node 103's East span 117 has failed (e.g.,severed lines). The stream of TDM traffic 113 is protection switched atnode 103. Node 103 informs the other nodes in the ring of the failure.The stream of TDM traffic 113 is transmitted back to node 101 from node103 in the protection channel 110 of node 103's West span 115. Thestream of TDM traffic 113 continues around the ring counter-clockwise tonode 105 along a protection path. The protection path includes theprotection channels 114, 120, 128, and 120 carrying traffic betweennodes 101 and 107, 107 and 109, 109 and 111, and 111 and 105respectively.

FIG. 1C is a diagram of exemplary traffic flow in spans 115 and 117 ofthe ring illustrated in FIG. 1A or 1B while there is not a failure. InFIG. 1C, transmit working channel 137, protection channels 110 receivingworking channel 119, and protection channel 139 of node 103's West span115 are shown. Similarly, transmit working channel 121 and transmitprotection channel 135, receiving working channel 141 and protectionchannel 143 of node 103's East span 117 are shown. The transmit workingchannel 137 and the receiving protection channel 139 of node 103's Westspan 115 are not shown in FIGS. 1A and 1B for simplicity. The transmitprotection channel 135 and the receiving working channel 141 of node103's East span 117 are also not shown in FIGS. 1A and 1B forsimplicity. A stream of working TDM traffic 104 is transmitted in thetransmit working channel 137 from node 103 to node 101. Another streamof working TDM traffic 113 is received in the receiving working channel119 and transmitted to node 105 in the transmit working channel 121while there is not a failure. The receive working channel 141 carriesTDM traffic not shown in the figure.

FIG. 1D is a diagram of exemplary traffic flow in spans 115 and 117 ofthe ring illustrated in FIGS. 1A and 1B while there is a failure. InFIG. 1D, the stream of working TDM traffic 104 continues to betransmitted in the transmit working channel 137. The stream of TDMtraffic 113 is protection switched to the transmit protection channel110 while there is a failure.

The ring described in FIGS. 1A-1D can be a 2 fiber or 4 fiber BLSR. Thechannels described in FIGS. 1A-1D are logical channels which may resideon different optical fibers depending on the ring architecture. A ringswitch, which is a protection switch that occurs in both 2 fiber and 4fiber BLSRs, is illustrated in FIGS. 1C-1D.

FIG. 1E is a diagram illustrating a span switch while the transmitworking channel 121 of FIGS. 1C-1D fails. In FIG. 1E, the transmitworking channel 121 of node 103 fails. In a 4 fiber optical ring, thefailure is detected and the stream of TDM traffic 113 is span switchedto the transmit protection channel 135. A span switch is a protectionswitch which occurs in a 4 fiber BLSR. Physically, the East span 117 is2 fibers. The transmit working channel 121 exists on one fiber and thetransmit protection channel 135 exists on a separate fiber. The failureof the working channel 121 is a failure of the first fiber. The streamof TDM traffic 113 is switched from being transmitted over the firstfiber to being transmitted over the second fiber.

High speed optical rings offer large amounts of bandwidth, but theprotection scheme utilizes 50% of that bandwidth. This 50% of totalbandwidth for a protection channel often goes unused while there is nota failure. It is often unused because traffic transmitted in theprotection channel would be preempted by the working TDM traffic while afailure occurs.

FIGS. 2A and 2B are diagrams illustrating the use of a protectionchannel to carry extra (TDM) traffic while there is and is not afailure. FIG. 2A is a diagram illustrating the use of a protectionchannel to carry extra TDM traffic while there is not a failure. In FIG.2A, a West span 201 is divided into a working channel 205 and aprotection channel 207. The working channel 205 carries TDM traffic 209and the protection channel 207 carries extra TDM traffic 211. An Eastspan 203 is also divided into a working channel 204 and a protectionchannel 206. The working channel 204 of the East span 203 carries TDMtraffic 213 and the protection channel 206 carries extra TDM traffic215.

FIG. 1A is a diagram of exemplary traffic flow on the ring while thereis not a failure. FIG. 1B is a diagram of exemplary traffic flow on thering while there is a failure. FIG. 1C is a diagram of exemplary trafficflow in spans 115 and 117 of the ring illustrated in FIG. 1A or 1B whilethere is not a failure. FIG. 1D is a diagram of exemplary traffic flowin spans 115 and 117 of the ring illustrated in FIGS. 1A and 1B whilethere is a failure. FIG. 1E is a diagram illustrating a span switchwhile the transmit working channel 121 of FIGS. 1C-1D fails. FIG. 2A isa diagram illustrating the use of a protection channel to carry extraTDM traffic while there is not a failure. In FIG. 2B, the East span 203has failed. The working TDM traffic 213 is protection switched into theprotection channel 207 of the West span 201. The protection switchedworking TDM traffic 213 preempts the extra TDM traffic 211 which waspreviously carried in the protection channel 207 of the West span 201.The extra TDM traffic 215 previously transmitted over the protectionchannel 207 of the East span 203 is not protected and is thereforecompletely lost upon the failure.

Extra TDM traffic is problematic to sell to customers because it ispreemptable and unprotected. A consumer could purchase the extra trafficservice from two network owners or providers and alternate between thetwo upon failures. While the above is true for a 2 fiber BLSR, theimpact to extra TDM traffic in a 4 fiber BLSR depends on the type offailure. In particular, while a ring switch in 4 fiber BLSR operates ina similar manner as described above, a span switch in a 4 fiber BLSRdoes not impact the extra TDM traffic transmitted on the non-failingspans.

SUMMARY OF THE INVENTION

The invention provides a method and apparatus for a variable rate pipeon a linear connections. According to one aspect of the invention, amethod is provided which provisions a pipe from a part of a workingchannel and at least a part of a protection channel of an M:N linearconnection. While there is not a failure in the linear connection, themethod provides for load balancing layer 2/3 traffic that is transmittedin the pipe. When there is a failure in the linear connection, thepipe's bandwidth is reduced and layer 2/3 traffic is load balanced forthe reduced pipe. Furthermore, the method provides for transmitting loadbalanced layer 2/3 traffic in the reduced pipe while there is a failure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1A is a diagram of exemplary traffic flow on the ring while thereis not a failure.

FIG. 1B is a diagram of exemplary traffic flow on the ring while thereis a failure.

FIG. 1C is a diagram of exemplary traffic flow in spans 115 and 117 ofthe ring illustrated in FIG. 1A or 1B while there is not a failure.

FIG. 1D is a diagram of exemplary traffic flow in spans 115 and 117 ofthe ring illustrated in FIGS. 1A and 1B while there is a failure.

FIG. 1E is a diagram illustrating a span switch while the transmitworking channel 121 of FIGS. 1C-1D fails.

FIG. 2A is a diagram illustrating the use of a protection channel tocarry extra TDM traffic while there is not a failure.

FIG. 2B illustrates preemption of extra TDM traffic while there is afailure.

FIG. 3 is a conceptual diagram illustrating an exemplary division of anoptical span's bandwidth according to one embodiment of the invention.

FIG. 4A is a diagram illustrating an example traffic flow while there isnot a failure in an optical span according to one embodiment of theinvention.

FIG. 4B is a diagram illustrating an example traffic flow while there isa failure in an optical span according to one embodiment of theinvention.

FIG. 4C is a diagram of the example traffic flow 419 of FIGS. 4A and 4Bwhile there is not and is a failure of the span 403 of FIGS. 4A an 4B ina ring according to one embodiment of the invention.

FIG. 5 is a diagram of circuit components in a hybrid network elementaccording to one embodiment of the invention.

FIG. 6 is a flowchart for allocating a layer 2/3 pipe and subpipes in anoptical ring according to one embodiment of the invention.

FIG. 7A illustrates traffic flowing through the BLSR while there is nota failure according to one embodiment of the invention.

FIG. 7B illustrates the example traffic flow through the BLSR whilethere is a failure before a routing protocol detects the failureaccording to one embodiment of the invention.

FIG. 7C illustrates the example traffic flow through the BLSR whilethere is a failure after the routing protocol detects the failureaccording to one embodiment of the invention.

FIG. 8A illustrates varying concatenations over the BLSR of FIGS. 7A-7Cwhile there is not a failure according to one embodiment of theinvention.

FIG. 8B illustrates a failure in the BLSR according to one embodiment ofthe invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the invention. However, it isunderstood that the invention may be practiced without these specificdetails. In other instances, well-known circuits, structures andtechniques have not been shown in detail in order not to obscure theinvention.

A method and apparatus is described that provides a pipe through anoptical ring network that includes some bandwidth from the working andprotection channels while there is no failure, but that is notcompletely lost on a failure. In this ring network, network elements areused that can transmit and receive TDM ring traffic. In addition, atleast certain of the network elements provide two different switchingtechniques—TDM and packet. The packet switching provided can support anynumber of protocols including layer 2 and layer 3 type protocols such asATM, Ethernet, Frame Relay, etc. In addition to typical operations of aTDM network element, the network elements are implemented to be ableto: 1) programmably select on an STS basis certain of the incoming TDMtraffic to be extracted and packet switched rather than TDM switched;and/or 2) receive packet traffic in another form and to be packetswitched. Regardless of which switching technique is used, the switchedtraffic going back onto the ring is put in TDM format and transmittedout. However, each time traffic is packet switched, that traffic can bestatistically multiplexed (e.g., the packets can be selectively droppedbased on various criteria). An exemplary implementation of such hybridnetwork elements is provided in FIG. 5.

FIG. 3 is a conceptual diagram illustrating an exemplary division of anoptical span's bandwidth according to one embodiment of the invention.In FIG. 3, the optical span's 301 bandwidth is evenly split between aworking channel 303 and a protection channel 305. A port 307 of theworking channel 303 will carry TDM traffic. This part of the workingchannel 303 will be referred to as the working TDM pipe 307. While thereis not a failure, the remaining port 309 of the working channel 303forms a subpipe (“working layer 2/3 subpipe”) and all of the protectionchannel 305 forms a subpipe. Together these subpipes form a layer 2/3pipe to transmit TDM traffic having layer 2/3 traffic (ATM, Ethernet,Frame Relay, Internet Protocol, etc.) as payload. While there is afailure, a port 313 of the protection channel 305 will carry aprotection switched stream of TDM traffic. A port 311 of the protectionchannel 305 will be used as a protecting layer 2/3 subpipe to carryanother stream of protection switched TDM traffic that has layer 2/3traffic as payload. The working layer 2/3 subpipe 309 will carry the TDMtraffic having layer 2/3 traffic as payload transmitted in the layer 2/3pipe while there is not a failure.

FIGS. 4A-4C are diagrams illustrating example traffic flow while thereis and is not a failure on an optical span according to one embodimentof the invention. FIG. 4A is a diagram illustrating an example trafficflow while there is not a failure in an optical span according to oneembodiment of the invention. In FIG. 4A, a West transmit span 401 isdivided into a working channel 405 and a protection channel 407. In FIG.4A, the West transmit span 401 carries two streams of traffic. In aworking TDM pipe 402 the West transmit span 401 carries a stream of TDMtraffic 409. The West transmit span 401 carries another stream of TDMtraffic 411 having layer 2/3 traffic as payload in a layer 2/3 pipe 412.The stream of TDM traffic 411 s represented by two lines to show thelayer 2/3 pipe 412 encompassing a segment of the working channel 405 andall of the protection channel 407 (it should be noted that the layer 2/3pipe need not encompass all of the protection channel 407—some of thischannel could go unused and/or some of this channel could be used for adifferent purpose, e.g., extra traffic).

In FIG. 4A, an East transmit span 403 is also divided into a workingchannel 406 and a protection channel 408. The East transmit span 403carries two streams of traffic. In a working TDM pipe 404 the Easttransmit span 403 carries a stream of TDM traffic 417. The East transmitspan 403 carries another stream of TDM traffic 419 having layer 2/3traffic as payload in a layer 2/3 pipe 414. The stream of TDM traffic419 is represented by two lines to show the layer 2/3 pipe 414encompassing a segment of the working channel 406 and all of theprotection channel 408 (again, it should be noted that the layer 2/3pipe need not encompass all of the protection channel 408).

The streams of TDM traffic 411 and 419 carry data traffic formattedaccording to a layer 2/3 protocol such as ATM, Ethernet, Frame Relay,Internet Protocol, etc as payload. The streams of TDM traffic 411 and419 can be transmitted in a number of scenarios. The streams of TDMtraffic 411 and 419 may be switched into the ring through the packetswitching mechanism in one node and exit the ring as TDM traffic fromanother node. The streams of TDM traffic 411 and 419 maybe switched intothe ring as layer 2/3 traffic through the packet switching mechanism inone node and exit the ring through the packet switching mechanism inanother node in the form of layer 2/3 traffic. These examples aredescribed as illustrations to aid in understanding the invention and notmeant to be limiting upon the invention.

FIG. 4B is a diagram illustrating an example traffic flow while there isa failure in an optical span according to one embodiment of theinvention. In FIG. 4B, the East transmit span 403 fails (e.g. a severedline, failing hardware, etc.). The West transmit span 401 continues tocarry the stream of TDM traffic 409 in the working TDM pipe 402. TheWest transmit span 401 also continues to carry the stream of TDM traffic411 having layer 2/3 traffic as payload, but only in a working layer 2/3subpipe 433. A protecting layer 2/3 subpipe 435 now carries the streamof TDM traffic 419 having layer 2/3 traffic as payload because alltraffic traveling in the working channel 406 of the East transmit span403 prior to the failure was protection switched to the protectionchannel 407 of the West transmit span 401. The East stream of TDMtraffic 417 now travels in the protecting TDM pipe 410 of the Westtransmit span 401. The West protecting TDM pipe 410 is the same size ornumber of timeslots as the working TDM pipe 404.

As shown in the illustration of FIGS. 4A and 4B, the streams of TDMtraffic 409 and 417 are transmitted at a constant rate because theyutilize the same amount of bandwidth while there is not and is afailure. In contrast, the streams of TDM traffic 411 and 419 aretransmitted at a variable rate. While a failure does not exist, bothstreams of TDM traffic 411 and 419 are transmitted over the layer 2/3pipe which is allocated a large segment of bandwidth including some ofthe working channel and possibly all of the protection channeltimeslots. While a failure exists, the streams of variable rate TDMtraffic 411 and 419 are transmitted over layer 2/3 subpipes which areallocated an equal amount of the timeslots not used by the constant rateTDM traffic 409 and 417, hence the layer 2/3 pipe is reduced.

The variability in the pipe size is possible because of the statisticalmultiplexing capability of the packet switching mechanism in the networkelements of the ring. Specifically, the reduction in the amount ofavailable bandwidth for the TDM traffic having layer 2/3 traffic aspayload requires the packet switch of the network element to bufferand/or to drop layer 2/3 traffic to make that traffic fit the providedpipe.

FIG. 4C is a diagram of the example traffic flow 419 of FIGS. 4A and 4Bwhile there is not and is a failure of the span 403 of FIGS. 4A an 4B ina ring according to one embodiment of the invention. In FIG. 4C, threenodes 431, 439, and 441 are coupled with each other to form an opticalring. Each node in the ring has a West and East transmit span, but inFIG. 4C only the East and West transmit spans from the node 431 and anEast transmit span from the node 439 are shown. The West transmit span401 carries traffic from node 431 to node 439. The East transmit span403 carries traffic from the node 431 to the node 441. The East transmitspan 440 carries traffic from the node 439 to the node 441. Aspreviously shown in FIG. 4A, the variable rate TDM traffic 419 travelsover the layer 2/3 subpipe 414 to node 441. Once node 431 's Easttransmit span 403 fails, the variable rate TDM traffic 419 travels overthe protecting layer 2/3 subpipe 435. Since the variable rate TDMtraffic 419 is destined for node 441, the variable rate TDM traffic 419is switched through node 439 and travels along node 439's East transmitspan 440 in its protecting layer 2/3 subpipe 443. Node 439 knows totransmit the variable rate TDM traffic 419 onto a protecting layer 2/3subpipe because node 431 has communicated to node 439 a protectionswitch.

As an illustration of the protection switch in relation to end users,assume that traffic from a first, second, and third user enter the ringillustrated in FIG. 4C at node 431. Also assume that the first andsecond user's traffic is to be terminated at node 441 and exit the ringat node 441 to an external network element. The third user is to beterminated at node 439 and exit the ring to an external network element.The traffic from all three users is transmitted over the layer 2/3 pipefrom node 431 to node 441. The traffic from the third user is switchedthrough the packet mesh of node 441 and transmitted over a second layer2/3 pipe (not shown) between node 441 and node 439. As before, assumethat there is a failure of span 403. While there is this failure, thetraffic in the layer 2/3 pipe 414 is switched to the protecting layer2/3 pipe 435. The traffic from all three users is passed through thecross connect of node 439 and terminated at node 441. The traffic fromthe first and second users exit the ring at node 441 while the trafficfrom the third user is switched through the packet mesh of node 441 andtransmitted back to node 439 over the working subpipe of the secondlayer 2/3 pipe (not shown).

As illustrated in FIG. 4C, a failure on the ring does not cause the lossof the traffic on the layer 2/3 pipe, just a reduction in the availablebandwidth. This is because the layer 2/3 pipe is made partially from theworking channel and partially from the protection channel. As such, thislayer 2/3 pipe is more sellable to customers than the extra trafficdescribed in the background section because a failure does not result ina total loss of service. Moreover, using the BLSR protection schemeenables the traffic traveling in the layer 2/3 pipe to be protectionswitched in a 50 millisecond time frame.

To provide an example of the manner in which the layer 2/3 pipe could besold, assume that the working and protection channel parts of the layer2/3 pipe 414 are respectively 30 mbps and 90 mbps. Assume, that each ofthe first, second and third users above want an equal amount ofbandwidth of the layer 2/3 pipe 414. Each customer could be offered aguaranteed (in the event of a single failure) 10 mbps and a maximum of40 mbps. The customers traffic at node 431 would be statisticallymultiplexed to fit the size of the layer 2/3 pipe currently beingprovided. The guaranteed 10 mbps per customer would be provided by theworking subpipe on span 403 or the protecting layer 2/3 subpipe 435. Themaximum 30 mbps per customer would be provided by the protection subpipeon span 403 while there is no failure. In this manner partially BLSRprotected layer 2/3 traffic is provided around the ring.

It should be understood that the ability to offer a guaranteed minimumbandwidth requires that the bandwidth of the layer 2/3 pipes on the ringnot be oversold. Thus, in the above example, to offer the third user theservice identified above, the ring provider would also have at least theneeded bandwidth (guaranteed 10 mbps and a maximum of 40 mbps) on thesecond layer 2/3 pipe from node 441 to node 439 (not shown) because thethird users traffic must traverse that span as well as span 403. Inother words, if a potential user's traffic must traverse multiple spansof the ring in layer 2/3 pipes, each of these layer 2/3 pipes must haveavailable the necessary bandwidth.

It should also be noted that not every network element in the ring needto be of the type that is capable of both TDM and packet switching (ahybrid network element). Specifically, while node 431 must be a hybridnetwork element, the node 439 could be a standard TDM network elementcapable of only performing TDM switching. Thus, compatibility ismaintained.

FIG. 5 is a diagram of circuit components in a hybrid network elementaccording to one embodiment of the invention. While in this embodimentseparate switching mechanisms are provided for the TDM and packetswitching (namely a TDM switch fabric and a packet mesh), alternativeembodiments could provide a single switching mechanism and/or differentswitching mechanisms (e.g., a packet switch fabric, a TDM mesh, etc.).In FIG. 5, four optical transmit fibers 515, 502, 506, 510 connect tophysical ports 515, 502, 506, and 510 respectively. Four optical receivefibers 517, 504, 508, and 512 connect to physical ports 513, 516, 520,and 523 respectively. TDM traffic is received over the optical receivefibers 517, 504, 508, 512 and transmitted over the optical transmitfibers 511, 514, 518, 522. The TDM traffic is transmitted and receivedas optical signals by physical connection circuitry (PCC) 501, 507, 503,505. The PCCs convert optical signals to electrical signals and viceversa for reception and transmission. The TDM traffic is transmitted andreceived between the PCCs 501, 507, 503, 505 and the TDM processingcircuits (TPCs) 519, 531, 525, and 537 respectively as electricalsignals. The TPCs transmit and receive TDM traffic from a control card(CC) 509. In another embodiment of the invention, each TPC and PCC islocated on a single processing element, such as an application specificintegrated circuit (ASIC). A hybrid network element is described in moredetail in a patent application titled “A Method and Apparatus forSwitching Data of Different Protocols” to David Stiles, filed on Mar.30, 2001, Ser. No.: 09/823,480, Attorney Docket Number: 004906. P002,which is hereby incorporated by reference.

The layer 2/3 traffic can be switched through the CC 509 or a packetmesh 550. The TPCs are programmable to insert and extract particularSTSs that carry layer 2/3 traffic to be packet switched. If TDM trafficcontains layer 2/3 payload to be switched through the packet mesh 550,then the TPCs 519, 531, 525, and 537 extract the layer 2/3 payloadtraffic from the TDM traffic and transmit the layer 2/3 traffic toingress layer 2/3 processing circuitry 523, 535, 529, and 541respectively. The TPCs 519, 531, 525, and 537 also receive layer 2/3traffic from egress layer 2/3 processing circuitry 521, 533, 527, and539 respectively. For a variable rate layer 2/3 traffic pipe, the egresslayer 2/3 processing circuitry includes the ability to queue andstatistically multiplex layer 2/3 traffic before transmitting it to aTPC. The TPCs 519, 531, 525, and 537 process the layer 2/3 trafficplacing it into SONET/SDH frames for transmission in timeslots. The TPCs519, 531, 525, and 537 are programmable to insert and extract particularSTSs that carry the layer 2/3 traffic to be packet switched.

The CC 509 detects failures, maintains a BLSR state machine, and updatesthe TDM cross connect table in response to changes in the BLSR statemachine. The CC 509 also sends a message to update the logicalinterfaces for packet BLSR protection switching. Typically an interfaceis a physical interface or port. A logical interface is the logicalconnection from a first network element to another network element ornode which may or may not be adjacent to the first network element. Thelogical interface refers to a physical port or interface which can bechanged. In addition, the CC 509 sends messages to reprogram the TPCs tohandle a protection switch (e.g., reorient concatenations, redirectchannels to packet mesh and CC, etc.).

To provide an example of the reprogramming of the network elements tohandle a ring switch, assume that the ring of FIG. 4C is a 2 fiber OC-12BLSR (that is, 6 STSs for working and 6 STSs for protection in eachdirection). Also assume that each of the nodes of FIG. 4C is implementedas the network element illustrated in FIG. 5; that the PCC 501 of agiven node is connected through fiber to the PCC 503 of the adjacentnode; that the fibers 515 and 506 are the transmit fibers; that the PCC503 of node 431 is connected through fiber to PCC 501 of node 441; andthat the fibers 517 and 508 are the receive fibers. Table 1 belowillustrates the concatenations and the redirection of STSs programmed inthe TPCs 519 and 525 of each node while there is not and is a failure onspan 403. While There is Not a Failure While There is a Failure Node TDMLayer ⅔ Pipe TDM Layer ⅔ Pipe 431 On TPC 519 for On TPC 519 for On TPC519 for On TPC 519 for transmit fiber transmit fiber transmit fibertransmit fiber 515: X on 515: STS 2C on 515: X on 515: STS 2C onchannels 1-4, channels 5-6; channels 1-4; channels 5-6; where X is STS6C on STS 1 on STS 2C on some particular channels 7-12 channel 7channels 11-12 arrangement On TPC 525 for protecting protecting layer OnTPC 525 for transmit fiber TDM; ⅔ subpipe transmit fiber 506: STS 2C onSTS 3C on On TPC 525 for 506: STS 1 on channels 5-6; channels 8-10transmit fiber channel 1; STS 6C on protecting 506: Nothing STS 3C onchannels channels 7-12 TDM 2-4 On TPC 525 for transmit fiber 506:Nothing 441 On TPC 519 for On TPC 519 for On TPC 519 for On TPC 519 forreceive fiber receive fiber receive fiber receive fiber 517: STS 1 on517: STS 2C on 517: Nothing 517: Nothing channel 1; channels 5-6; On TPC525 for On TPC 525 for STS 3C on STS 6C on receive fiber receive fiberchannels 2-4 channels 7-12 508: Y on 508: STS 2C on On TPC 525 for OnTPC 525 for channels 1-4; channels 5-6; receive fiber receive fiber STS1 on STS 2C on 508: Y on 508: STS 2C on channel 7 channels 11-12channels 1-4, channels 5-6; protecting protecting layer where Y is STS6C on TDM; ⅔ subpipe some particular channels 7-12 STS 3C on channelsarrangement 8-10 protecting TDM 439 On TPC 519 for On TPC 519 for On TPC519 for On TPC 519 for transmit fiber transmit fiber transmit fibertransmit fiber 515: Y on 515: STS 2C on 515: Y on 515: STS 2C onchannels 1-4 channels 5-6; channels 1-4; channels 5-6; On TPC 525 forSTS 6C on STS 1 on STS 2C on receive fiber channels 7-12 channel 7channels 11-12 508: X on On TPC 525 for protecting protecting layerchannels 1-4 receive fiber TDM; ⅔ subpipe 508: STS 2C on STS 3C on OnTPC 525 for channels 5-6; channels 8-10 receive fiber STS 6C onprotecting 508: STS 2C on channels 7-12 TDM channels 5-6; On TPC 525 forSTS 2C on receive fiber channels 11-12 508: X on protecting layerchannels 1-4; ⅔ subpipe b STS 1 on channel 7 protecting TDM; STS 3C onchannels 8-10 protecting TDM

In addition to the reprogramming of the TPCs, the cross connect tablesand the logical interfaces are altered accordingly. As in the exampledescribed above, traffic for three users enter the ring at node 431 ofFIG. 4C. To extend this example, assume that the traffic from thesethree users is switching into the ring in node 431 from the PCC 507through the packet mesh 550, that the traffic from the first and seconduser is exiting the ring at node 441 through PCC 505 after beingswitched through the packet mesh 550, and that the traffic from thethird user is exiting the ring at node 439 through PCC 505 after beingswitched through the packet mesh 550. While there is not a failure, thetraffic from all three users is transmitted from the IL2/3PC 533 acrossthe packet mesh to the EL2/3PC 529 according to the forward tables,which refer to logical interfaces, and transmitted in the layer 2/3 pipeby TPC 525. While there is a failure of the fibers connecting into 431'sPCC 503, the logical interfaces are modified so that the traffic fromthe three users is switched through the packet mesh from IL2/3PC 533 tothe EL2/3PC 523 and transmitted in the protecting layer 2/3 pipe to node439 by the TPC 519 which has been reprogrammed as described above.

In node 439, while there is not a failure, the traffic from the thirduser is received at the IL2/3PC 521 and switched through the packet meshto EL2/3PC 541. While there is a failure, the node 439 is modified sothat the traffic for the three users received from node 431 on node439's PCC 503 in the protecting layer 2/3 channel is switched to theprotecting layer 2/3 channel to node 441. This switch will go throughthe cross connect, and is in fact a BLSR pass-through. An additionalchange for the dropping of the third users traffic is in the nextparagraph.

In node 441, while there is not a failure, the traffic from all threeusers is received at the IL2/3PC 521 and switched through the packetmesh: the first and second users' traffic is switched to EL2/3PC 541,while the third user's traffic is switched to EL2/3PC 529. While thereis a failure between two adjacent nodes, the logical interfaces aremodified because of the failure so that the traffic for the first andsecond users received from node 439 on node 441's PCC 503 is switchedthrough the packet mesh 550 from the IL2/3PC 527 to the EL2/3PC 541 andtransmitted out of the ring through the PCC 505. The traffic for thethird user is switched through the packet mesh from the IL2/3PC 527 tothe EL2/3PC 529 and transmitted out the PCC 503 on the working layer 2/3channel to node 439 by the TPC 525. The traffic from the third user isreceived at node 439 at the PCC 501 on the working layer 2/3 channel andswitched through the packet mesh 550 from the IL2/3PC 521 to the EL2/3PC541 in accordance with the forwarding tables and transmitted out of thering by the PCC 505.

To provide another example of the reprogramming of the TPCs to handle aprotection switch, assume that the ring of FIG. 4C is a 4 fiber OC-48BLSR. In a 4 fiber implementation of the invention, a load balancingmechanism would be implemented to balance traffic between the workinglayer 2/3 channel and the protecting layer 2/3 channel (e.g., multi-linkPPP, ATM SAR, etc.). Also assume that each of the nodes of FIG. 4C isimplemented as the network element illustrated in FIG. 5; that the PCCs501 and 507 are the transmit and receive pair respectively for the Eastspan; and that the PCCs 503 and 505 are the transmit and receive pairrespectively for the West span.

Thus, while there is a failure requiring a ring switch on the East spanof a node: 1) traffic coming in PCC 505 is protection switched to PCC503; and 2) the redirect/concatenations of the TPCs 519 and 531 must bealtered. Whereas while there is a failure requiring a ring switch on theWest span of a node: 1) traffic coming in PCC 507 is protection switchedto PCC 501; and 2) the redirect/concatenations of the TPCs 525 and 537must be altered. In addition, while there is a failure requiring a ringswitch on a midspan node, the redirect/concatenations of the TPCs 531and 537 must be altered accordingly. The redirect/concatenations of theTCPs 519 and 525 are not affected because of the assumption that TPCs519 and 525 correspond to working channels.

To provide a more specific example, assume that while there is not afailure, node 431 transmits TDM traffic as STS-12 c and STS-24 c throughthe PCC 503 to node 441. The channels used for the STS-12 c and STS-24 ctraffic are collectively referred to as the working TDM pipe. Node 431transmits over the layer 2/3 pipe STS-12 c and STS-48 c of trafficthrough PCC 503 and PCC 505 respectively to node 441 of FIG. 4C. Thesame configuration of traffic is transmitted to node 439 from node 431through PCCs 501 and 507. If the span corresponding to PCC 503 is lost(e.g., the card having PCC 503 is removed, the fibers 506 and 508 aresevered, etc.), the control card 509 detects the failure, updates theBLSR state machine, and reprograms the TPC 537. The TPC 537 isreprogrammed to match the concatenations, channel redirects, etc., ofTPC 525. A span switch occurs so that the traffic previously transmittedover the span corresponding to PCC 503 now is transmitted over the spancorresponding to PCC 505. Hence the working TDM pipe and working layer2/3 pipe survive through PCC 505.

If both spans between nodes 431 and 441 (the span corresponding to PCC503 and the span corresponding to PCC 505) are lost (e.g. cables 506,508, 510 and 512 are severed, both cards having PCCs 503 and 505 arepulled, etc.), then a ring switch will occur. The control card 509 willdetect a failure of the spans between nodes 431 and 441. The controlcard 509 will update the BLSR state machine, reprogram TPC 531, and senda message to node 439 indicating the failure. The control card 509reprograms the TPC 531 to match the concatenations, channel redirects,etc., of TPC 525. Hence, traffic originally transmitted from node 431 tonode 441 through PCCs 503 are now transmitted through PCC 507.

On the nodes adjacent to the failure, the logical interfaces will bereprogrammed, but the destinations in the forwarding tables will not bechanged (This is an effect of having two switch mechanisms providingalternative paths; as such, this may not be required in otherimplementations). An alternative embodiment could be implemented with asingle path through the cross-connect. In such an alternativeembodiment, the packet mesh would be subordinate to the cross-connectsince all traffic including packet switched traffic would pass throughthe cross-connect when entering or exiting the box.

Embodiments of the invention are not limited to application in anoptical ring. The previously described load balancing mechanism cansupport an M:N protection scheme for protecting variable rate pipescarried over linear connections (e.g., the last mile, links betweenrings, etc.). Various embodiments of the invention can implement loadbalancing in an M:N protection scheme of a linear connection carryingoptical traffic and layer 2/3 traffic over the last mile, between rings,etc., by implementing multi-link PPP on all IL2/3PCs, implementingmulti-link PPP on a primary EL2/3PC, introducing additional hardware orcircuitry (e.g., an additional cross connect card), etc.

FIG. 6 is a flowchart for allocating a layer 2/3 pipe and subpipes in anoptical ring according to one embodiment of the invention. At block 601,a network administrator configures timeslots as working and protectionchannels on each node of a ring. At block 603, the network administratordetermines which timeslots will be processed as layer 2/3 traffic andwhich timeslots will be processed as TDM traffic. At block 605, a TDMprocess running on a control card of a node in the ring detects afailure in one of the node's spans. The TDM process updates a TDM crossconnect forwarding table managed on the control card at block 607. Atblock 609, the TDM process sends a message to a layer 2/3 processindicating the failure. The layer 2/3 process updates a protectioninterface table in response to the message from the TDM process at block611. At block 613, the node communicates the failure to other nodes inthe ring. At block 615, the other nodes in the ring update their crossconnect tables and logical interfaces in accordance with the failuredetected by the detecting node.

In another embodiment of the invention, the protection interface tableis a data structure with a reference to a logical working interface anda logical protection interface. The logical working interfacecorresponds to a physical port connecting to a transmit fiber to carrytraffic destined for a node X going in a preferred direction on thering. The logical protection interface corresponds to another physicalport connected to a transmit fiber destined for the node X, but going inthe opposite direction and possibly through other nodes in the ring. Alogical interface stored in or referenced by a layer 2/3 forwardingtable initially refers to the logical working interface while there isnot a failure. While there is a failure, the logical interface refers tothe logical protection interface. While the failure is corrected, thelogical interface is updated to refer to the logical working interface.In another embodiment of the invention, a routine manages logicalinterfaces and another routine manages alternate interfaces. A networkadministrator configures alternate interfaces on a network element. Thealternate interface manager will create a data structure to refer to 2logical interfaces which are managed by the interface manager. One ofthe interfaces will be the working interface while the other interfacewill be the protecting interface. In the layer 2/3 forwarding table, acircuit identifier is associated to either a logical interface or analternate interface. Upon a failure notification, the alternateinterface manager will alter the data structure to reference the logicalinterface acting as the protecting interface. In another embodiment ofthe invention, the TDM process instead of the layer 2/3 process updatesa data structure indicating protection interfaces.

The owner of the optical ring can now offer protected service tomultiple customers. Typically, only the traffic traveling in the workingchannel was sold to customers since consumers did not want to purchase aservice which may be interrupted (e.g., for days). Alternatively, aconsumer may choose to purchase at a reduced cost, the extra trafficservice from 2 providers. This consumer would alternate between theseproviders as failures occurred. With a layer 2/3 pipe, the owner of theoptical ring can offer multiple classes of service. In addition to thetraditional constant rate TDM traffic service, the network owner orprovider can offer a variable rate TDM traffic service to customersbecause the payloads are layer 2/3 units of traffic. For example, ifbandwidth corresponding to a layer 2/3 pipe transmits at a rate of 100megabits per second with 20 megabits corresponding to the layer 2/3subpipes, the owner or provider can offer a service guaranteeing a rateof 20 megabits per second with a maximum of 100 megabits per second.This variable rate service can be offered to multiple people since theTDM payloads are layer 2/3 units of traffic. In addition, the variablerate service can be offered with a BLSR protection time of 50milliseconds. Furthermore, the owner or provider of the optical network,is not forced to either donate or sell at a reduced cost 50% of theirbandwidth. The owner of provider can sell 100% of its bandwidth with thecombination of standard TDM service and the variable rate TDM service.

A continuum of embodiments exist for the invention. On one end of thecontinuum is an embodiment only utilizing BLSR protection. On the otherend of the continuum is an embodiment only utilizing layer 2/3protection. An embodiment utilizing BLSR protection has already beendescribed. Another embodiment of the invention representing the layer2/3 end of this continuum switches layer 2/3 traffic through the packetmesh of every hybrid network element of a BLSR. An embodiment of theinvention in a 2-fiber BLSR representing this other end of the continuumis described herein.

FIGS. 7A-7C illustrate an example of traffic flowing through a BLSRwhile there is and while there is not a failure according to oneembodiment of the invention. FIG. 7A illustrates traffic flowing throughthe BLSR while there is not a failure according to one embodiment of theinvention. In FIG. 7A, the BLSR includes five nodes 701, 703, 705, 707,and 709. The BLSR can be divided into two logical rings: an outer ringand an inner ring. Links 725, 733, 731, 729, and 727 form the inner ringand carry traffic in a counter-clockwise direction. Links 715, 717, 719,721, and 723 form the outer ring and carry traffic in a clockwisedirection. Each link is divided into a working channel 737 and aprotection channel 739 by a line 710. Each working channel 737 isconceptually divided into a working optical pipe 741 and a working layer2/3 pipe 743 separated by a dashed line 735. A set of layer 2/3 traffic711 enters the BLSR through the packet mesh of node 707. The set oftraffic is destined for node 701. In this example, the set of traffic isplaced on the outer ring path and transmitted over the protectionchannel 739 and the working layer 2/3 pipe 743 of the links 721 and 723to node 701. At node 701, the set of traffic 711 exits the ring throughthe packet mesh of node 701. A set of layer 2/3 traffic 713 also entersthe ring through the packet mesh of node 707. The set of traffic 713 isdestined for node 703. In this example, the set of traffic 713 is placedon the inner ring path and transmitted over the protection channel 739and working layer 2/3 pipe 743 of the links 729 and 727. The set oftraffic 713 exits the ring through the packet mesh of node 703.Additional traffic can enter and exit the ring though any of the fivenodes 701, 703, 705, 707 or 709, but only the sets of traffic 711 and713 are focused for ease of understanding.

FIG. 7B illustrates the example traffic flow through the BLSR whilethere is a failure before a routing protocol detects the failureaccording to one embodiment of the invention. In FIG. 7B, the spanbetween nodes 701 and 705 fails. The BLSR performs automatic protectionswitching in response to the failure. A line 740 indicates the divisionof the protection channel 739 into a protecting layer 2/3 pipe 744 and aprotecting optical pipe 742 on every link. Optically switched traffictraveling over the outer ring that would travel between nodes 701 and705 is switched to the protecting optical pipe 742 of the inner ring.Likewise, optically switched traffic traveling over the inner ring thatwould travel between nodes 701 and 705 is switched to the protectingoptical pipe 742 of the outer ring. Since the layer 2/3 traffictraveling on the ring is switched through the packet mesh of each node,it is not automatically switched to a new path. At this point in timewhile there is a failure, the routing protocol has not detected thefailure between nodes 701 and 705. Therefore, the set of traffic 711continues to be transmitted to node 705, but in a smaller bandwidthbecause of the protection switched traffic which now occupies theprotecting optical pipe 742 of the link 721. Until the routing protocolupdates forwarding tables in response to the ring failure, some of theset of traffic 711 is dropped at node 705. The set of traffic 713 istransmitted in a reduced pipe because of the BLSR automatic protectionswitch.

FIG. 7C illustrates the example traffic flow through the BLSR whilethere is a failure after the routing protocol detects the failureaccording to one embodiment of the invention. In FIG. 7C, the routingprotocol has recalculated a path for the set of traffic 711. Althoughany number of paths may result, this example describes the fastestalternative path as being through nodes 709 and 703. The set of traffic711 is no longer transmitted from node 707 to node 705. As a result ofrouting calculations, the set of traffic 711 is transmitted on the innerring. The sets of traffic 711 and 713 are statistically multiplexedtogether to be transmitted over the working layer 2/3 pipe and theprotecting layer 2/3 pipe on links 727 and 729 (i.e. the sets of traffic711 and 713 share the bandwidth provided by the working layer 2/3 pipeand the protecting layer 2/3 pipe). The multiplexed set of traffic isdenoted as traffic 712. At node 703, the set of traffic 713 is switchedout of the ring through the packet mesh of node 703. The set of traffic711 continues around the ring to node 701 over the link 725. At node701, the set of traffic 711 is switched out of the ring through thepacket mesh of node 701.

An embodiment of the invention utilizing layer 2/3 protection is able todeliver best-effort service and differentiated service level Quality ofService (QoS). An embodiment of the invention only utilizing BLSRprotection for all traffic on a BLSR is able to deliver guaranteedservice level QoS. Embodiments of the invention falling between thesetwo extremes are able to deliver a mixture of service level QoS.Best-effort service is basic connectivity without guarantees.Differentiated service does not offer a guarantee, but traffic istreated based on statistical preference. Various embodiments of theinvention can be applied to a network depending on the trafficcharacteristics of the network.

For example, if layer 2/3 traffic traveling over the ring is erratic oroccurs in bursts, an embodiment of the invention which provides forguaranteed bandwidth allows bandwidth to remain idle. For example,assume users A and B are guaranteed 10 Mbits/sec of bandwidth. Eventhough one user may only be using 2 Mbits/sec of bandwidth, the otheruser cannot go beyond 10 Mbits/sec of bandwidth. Embodiments of theinvention similar to that illustrated in FIGS. 7A-7C , statisticallymultiplex all traffic from users over the available bandwidth. Using theexample above, users A and B are provided 20 Mbits/sec of bandwidth. Ifone user only uses 2 Mbits/sec, then 18 Mbits/sec of bandwidth isavailable to the other user. In addition, switching traffic through thepacket mesh makes available the variety of services available with layer2/3 traffic (e.g., prioritization, traffic shaping, QoS signaling,etc.).

Furthermore, an embodiment of the invention utilizing layer 2/3protection allows varying pipe sizes around the ring. A networkadministrator can adjust the amount of working channel bandwidthallocated to the working optical pipe and the working layer 2/3 pipe inaccordance with traffic characteristics on a span by span basis. Theability to customize part of the ring increases efficient utilization ofthe ring.

FIGS. 8A-8B illustrate example provisioning of varying size pipes arounda BLSR and changing concatenations according to one embodiment of theinvention. To illustrate this example of varying pipe sized and changingconcatenations in the network elements to handle a ring switch, assumethat the ring of FIGS. 7A-7C is a 2 fiber OC-12 BLSR (6 STSs for workingand 6 STSs for protecting in each direction). Also assume that each ofthe nodes of FIGS. 7A-7C is implemented as the network elementillustrated in FIG. 5. FIG. 8A illustrates varying concatenations overthe BLSR of FIGS. 7A-7C while there is not a failure according to oneembodiment of the invention. In FIG. 8A, the BLSR of FIGS. 7A-7C hasvarying pipe sizes on each link. Each link is labeled with one of theletters A-C to identify the type of concatenation. Table 1 identifiesthe concatenations corresponding to each letter (concatenations in thisexample conform to current standards). In this example, the entireprotection channel is used for layer 2/3 traffic while there is not afailure. Hence, only the concatenations of the working channel trafficneed be identified because all traffic in the protection channel isconcatenated as STS-6 c in this example. In alternative embodiments,part of the protection channel can be used for other types of traffic.Optically switched traffic transmitted in the working channel is denotedas Wt. Layer 2/3 traffic transmitted in the working channel is denotedas Wp. TABLE 1 Concatenation of Pipes A B C Wt STS-1 STS-3c STS-3c,STS-1, STS-1 Wp STS-3c, STS-3c STS-1 STS-1, STS-1

The concatenations corresponding to the letter A provide for a largeramount of bandwidth to layer 2/3 traffic. The concatenationscorresponding to the letter C allot a larger amount of bandwidth tooptically switched traffic. The concatenations corresponding to theletter B evenly allocate bandwidth to layer 2/3 traffic and opticallyswitched traffic.

Table 2 identifies the concatenations for each link for both the innerring and the outer ring. Since only layer 2/3 traffic will travel in theprotection channels of the ring, the column with the header “Pt” remainsempty. TABLE 2 Concatenation of Traffic While There Is Not A Failure WtWp Pt Pp Inner Ring 701→705 STS-3c STS-3c STS-6c 705→707 STS-3c STS-3cSTS-6c 707→709 STS-3c STS-3c STS-6c 709→703 STS-3c, STS-1, STS-1 STS-6cSTS-1 703→701 STS-3c, STS-1, STS-1 STS-6c STS-1 Outer Ring 701→703STS-3c, STS-1, STS-1 STS-6c STS-1 703→709 STS-3c STS-3c STS-6c 709→707STS-3c STS-3c STS-6c 707→705 STS-1 STS-3c, STS-1, STS-6c STS-1 705→701STS-1 STS-3c, STS-1, STS-6c STS-1

FIG. 8B illustrates a failure in the BLSR according to one embodiment ofthe invention. In FIG. 8B, the links 801 and 811 connecting nodes 701and 705 fail. The BLSR performs an automatic protection switch inresponse to the failure of the links. The switch does not affect theconcatenations of the traffic transmitted in the working channels of thering (excluding the failed links). The concatenations of the traffictransmitted in the protection channels are adjusted for the automaticprotection switch as indicated in Table 3. TABLE 3 Concatenation ofTraffic While There Is A Failure Wt Wp Pt Pp Inner Ring 705→707 STS-3cSTS-3c STS-1 STS-3c, STS-1, STS-1 707→709 STS-3c STS-3c STS-1 STS-3c,STS-1, STS-1 709→703 STS-3c, STS-1, STS-1 STS-1 STS-3c, STS-1, STS-1STS-1 703→701 STS-3c, STS-1, STS-1 STS-1 STS-3c, STS-1, STS-1 STS-1Outer Ring 701→703 STS-3c, STS-1, STS-1 STS-3c STS-3c STS-1 703→709STS-3c STS-3c STS-3c STS-3c 709→707 STS-3c STS-3c STS-3c STS-3c 707→705STS-1 STS-3c, STS-1, STS-3c STS-3c STS-1

As illustrated in Table 3, the concatenations for the traffictransmitted over the protection channel are modified. The protectionchannels of the inner ring are adjusted based on the working trafficswitched from the outer ring. The protection channels of the outer ringare adjusted based on the working traffic switched from the inner ring.Since the Wt traffic which previously traveled over the outer ring linkbetween nodes 701 and 705 was transmitted as STS-1, then STS-1 of theprotection channel of the inner ring is used for the protection switchedtraffic. Likewise, since the Wt traffic which previously traveled overthe inner ring link between nodes 701 and 705 was transmitted as STS-3c, then STS-3 c of the protection channel of the outer ring is used forthe protection switched traffic from the inner ring. Hence, each node'sTPC transmitting traffic in the protection channel through the innerring is reprogrammed from transmitting STS-3 c of layer 2/3 traffic totransmitting STS-1 of optically switched traffic, 2 STS-1 s of layer 2/3traffic, and an STS-3 c of layer 2/3 traffic. Each node's TPCtransmitting traffic in the protection channel of the outer ring isreprogrammed from transmitting STS-6 c of layer 2/3 traffic totransmitting an STS-3 c of layer 2/3 traffic and an STS-3 c of opticallyswitched traffic.

As indicated above, such an embodiment of the invention can also beapplied to a 4-fiber BLSR or n-fiber BLSR.

The techniques shown in the figures can be implemented using code anddata stored and executed on computers. Such computers store andcommunicate (internally and with other computers over a network) codeand data using machine-readable media, such as magnetic disks; opticaldisks; random access memory; read only memory; flash memory devices;electrical, optical, acoustical or other form of propagated signals(e.g., carrier waves, infrared signals, digital signals, etc.); etc. Ofcourse, one or more parts of the invention may be implemented using anycombination of software, firmware, and/or hardware.

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described. Although the invention has beendescribed with reference to the TDM form of optical switching, theinvention can be applied to any form of optical switching including wavedivision multiplexing, dense wave division multiplexing, etc. Inaddition, the invention has been described with respect to a 2 fiber and4 fiber BLSR, but can be scaled to other n-fiber architectures of BLSR.

Furthermore, while the invention has been described in terms ofswitching the traffic in the layer 2/3 pipe through the packet mesh ofeach node while there is not a failure, a variety of configurations arepossible for an optical ring with a layer 2/3 pipe. In a five node ring,a first node may have a layer 2/3 pipe defined over a direct connectionto a second node. The first node may also have a layer 2/3 pipe definedover a logical direct connection to a third node through the crossconnect of the second node. The first node may also have a layer 2/3pipe defined over a logical direct connection to a fifth node throughthe fourth node's cross connect. An optical ring may have 4 nodes whichare hybrid network elements and 2 nodes which are TDM only networkelements. The TDM only network elements may only act as regeneratorsbetween the hybrid network elements. A first hybrid node may have alayer 2/3 pipe defined to a second layer 2/3 pipe through a TDM onlynode. The first hybrid node may have a layer 2/3 pipe defined to the TDMonly node while a another layer 2/3 pipe is defined from the TDM onlynode to the second hybrid node. These examples are provided to aid inthe understanding of the invention and not meant to be limiting upon theinvention.

In addition, although the traffic that is passing through a given node(being provided to that node on a span of the ring and being transmittedby that node out another span of the ring) in layer 2/3 pipes may beswitched through the packet mesh of that node, the traffic is notconsidered to be terminated from the ring at that node, but is ratherconsidered to still be on the ring (similar to the manner in whichvirtual tributaries (VTs) are considered to not be terminated from thering). However, since each packet is addressed individually, squelchingis not needed as with a VT ring. The method and apparatus of theinvention can be practiced with modification and alteration within thespirit and scope of the appended claims. The description is thus to beregarded as illustrative instead of limiting on the invention.

1. A computer implemented method comprising: provisioning a pipe from apart of a working channel and at least part of a protection channel ofan M:N linear connection; load balancing layer 2/3 traffic transmittedin the pipe while there is not a failure; reducing the pipe's bandwidthwhen the failure occurs in the M:N linear connection; load balancinglayer 2/3 traffic for the reduced pipe; and transmitting the loadbalanced layer 2/3 traffic in the reduced pipe while there is thefailure.
 2. The computer implemented method of claim 1 wherein the loadbalancing is performed in accordance with multi-link PPP.
 3. Thecomputer implemented method of claim 1 wherein the load balancing isperformed in accordance with ATM SAR.
 4. The computer implemented methodof claim 1 wherein the working channel and the protection channel areprovisioned from a set of three or more optical fibers.
 5. The computerimplemented method of claim 1 wherein the linear connection couples afirst optical ring with a second optical ring.
 6. The computerimplemented method of claim 1 wherein layer 2/3 traffic is InternetProtocol traffic.
 7. The computer implemented method of claim 1 whereinlayer 2/3 traffic is ATM traffic.
 8. A network element comprising: acontrol card to allocate a pipe from a working channel and at least partof a protection channel of an M:N linear connection, to detect failuresin the M:N linear connection, to reduce the pipe's bandwidth when afailure occurs in the M:N linear connection; a layer 2/3 processingcircuitry coupled with the control card, the layer 2/3 processingcircuitry to host a load balancing process and to transmit layer 2/3traffic in accordance with the load balancing process; and an opticalprocessing circuitry coupled with the control card and the layer 2/3processing circuitry, the optical processing circuitry to encapsulatelayer 2/3 traffic within optical traffic.
 9. The network element ofclaim 8 wherein the linear connection couples a first optical ring witha second optical ring.
 10. The network element of claim 8 wherein thelayer 2/3 processing circuitry is a packet processing ASIC.
 11. Thenetwork element of claim 8 wherein the optical processing circuitry is aTDM ASIC.
 12. The network element of claim 8 wherein the opticalprocessing circuitry is a DWDM ASIC.
 13. The network element of claim 8wherein the load balancing process is performed in accordance withmulti-link PPP.
 14. The network element of claim 8 wherein the loadbalancing process is performed in accordance with ATM SAR.
 15. Thenetwork element of claim 8 wherein the layer 2/3 processing circuitry isan ingress layer 2/3 processing circuitry.
 16. The network element ofclaim 8 wherein the layer 2/3 processing circuitry is a primary egresslayer 2/3 processing circuitry.
 17. A network element comprising: acontrol card to allocate a pipe from a working channel and at least partof a protection channel of an M:N linear connection, to detect failuresin the M:N linear connection, to reduce the pipe's bandwidth when afailure occurs in the M:N linear connection; an egress layer 2/3processing circuitry coupled with the control card, the egress layer 2/3processing circuitry to process layer 2/3 traffic for transmission inthe pipe; an ingress layer 2/3 processing circuitry coupled with theegress layer 2/3 processing circuitry, the ingress layer 2/3 processingcircuitry to host a load balancing process and to transmit layer 2/3traffic to the egress layer 2/3 processing circuitry in accordance withthe load balancing process; and an optical processing circuitry coupledwith the control card, the ingress layer 2/3 processing circuitry andthe egress layer 2/3 processing circuitry, the optical processingcircuitry to encapsulate layer 2/3 traffic within optical traffic. 18.The network element of claim 17 wherein the linear connection couples afirst optical ring with a second optical ring.
 19. The network elementof claim 17 wherein the layer 2/3 processing circuitry is a packetprocessing ASIC.
 20. The network element of claim 17 wherein the opticalprocessing circuitry is, a TDM ASIC.
 21. The network element of claim 17wherein the optical processing circuitry is a DWDM ASIC.
 22. The networkelement of claim 17 wherein the load balancing process is per formed inaccordance with multi-link PPP.
 23. The network element of claim 17wherein the load balancing process is performed in accordance with ATMSAR.
 24. A network element comprising: a control card to allocate a pipefrom a working channel and a protection channel of an M:N linearconnection, to detect failures in the M:N linear connection, to reducethe pipe's bandwidth when a failure occurs in the M:N linear connection;an ingress layer 2/3 processing circuitry coupled with the control card,the ingress layer 2/3 processing circuitry receive layer 2/3 traffic, toforward the layer 2/3 traffic to a primary egress layer 2/3 processingcircuitry; the primary egress layer 2/3 processing circuitry coupledwith the ingress layer 2/3 processing circuitry, the primary egresslayer 2/3 processing circuitry to host a load balancing process and totransmit layer 2/3 traffic in accordance with the load balancingprocess; an egress layer 2/3 processing circuitry coupled with theprimary egress layer 2/3 processing circuitry, the egress layer 2/3processing circuitry to process layer 2/3 traffic received from theprimary egress layer 2/3 processing circuitry for transmission in thepipe; and an optical processing circuitry coupled with the control card,the egress layer 2/3 processing circuitry and the primary egress layer2/3 processing circuitry, the optical processing circuitry toencapsulate the set of layer 2/3 traffic within optical traffic.
 25. Thenetwork element of claim 24 wherein the linear connection couples afirst optical ring with a second optical ring.
 26. The network elementof claim 24 wherein the layer 2/3 processing circuitry is a packetprocessing ASIC.
 27. The network element of claim 24 wherein the opticalprocessing circuitry is a TDM ASIC.
 28. The network element of claim 24wherein the optical processing circuitry is a DWDM ASIC.
 29. The networkelement of claim 24 wherein the load balancing process is performed inaccordance with multi-link PPP.
 30. The network element of claim 24wherein the load balancing process is performed in accordance with ATMSAR.
 31. A machine-readable medium that provides instructions, whichwhen executed by a set of one or more processors, cause said set ofprocessors to perform operations comprising: provisioning a pipe from apart of a working channel and at least part of a protection channel ofan M:N linear connection; load balancing layer 2/3 traffic transmittedin the pipe while there is not a failure; reducing the pipe's bandwidthwhen the failure occurs in the M:N linear connection; load balancinglayer 2/3 traffic for the reduced pipe; and transmitting the loadbalanced layer 2/3 traffic in the reduced pipe while there is thefailure.
 32. The machine-readable medium of claim 31 wherein the loadbalancing is performed in accordance with multi-link PPP.
 33. Themachine-readable medium of claim 31 wherein the load balancing isperformed in accordance with ATM SAR.
 34. The machine-readable medium ofclaim 31 wherein the working channel and the protection channel areprovisioned from a set of three or more optical fibers.
 35. Themachine-readable medium of claim 31 wherein the linear connectioncouples a first optical ring with a second optical ring.
 36. Themachine-readable medium of claim 31 wherein layer 2/3 traffic isInternet Protocol traffic.
 37. The machine-readable medium of claim 31wherein layer 2/3 traffic is ATM traffic.